人工浅場の地形変化特性と浅場内部の間隙水圧変動に関する実験的研究  [in Japanese] EXPERIMENTAL STUDY ON TOPOGRAPHIC CHANGE OF ARTIFICIAL SHALLOW AND PORE-WATER PRESSURE ON SURFACE LAYER OF ARTIFICIAL SHALLOW  [in Japanese]

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Abstract

人工浅場の地形変化特性を浅場表面の底面流速と浅場表層の間隙水圧に着目して水理実験により検討した.その結果,浅場に地形変化が生じる範囲は入射波波高や入射波周期の増大に伴って広がることを確認した.また,浅場を構成する底質粒子が細粒径の場合には,Shields数と相対鉛直有効応力比の間に負の相関があり,底面流速が岸向きの位相では相対鉛直有効応力比が減少し,逆に底面流速が沖向きの位相では相対鉛直有効応力比が増加することを明らかにし,そのために沖向きの底質移動は底質粒子間の拘束力が弱まることで助長される可能性を示唆した.さらに,そのような条件下では,間隙水圧の影響を考慮した修正Shields数により底質移動をより適切に評価できる可能性を示し,底質移動とそれに伴う地形変化を検討する際における底質表層の間隙水圧の重要性を示した.

 Topographic change of an artificial shallow is investigated experimentally in terms of bottom flow velocity on the surface of the shallow and pore-water pressure on the surface layer of the shallow. Experimental results show that the erosion occurs from the upper part of the slope to the offshore part of the crown, which corresponds to a breaking point judged from the spatial distributions of the wave height and the mean water level. It is also found that the area of the topographic change increases with an incident wave height and an incident wave period. For the shallow composed of fine sediments, a relative vertical effective stress ratio (RVESR) reduces during onshore bottom flow velocity while the RVESR rises during offshore bottom flow velocity, and suggest that offshore sediment transport can be accelerated because it is inferred that restricting force between sediment particles decreases with the increase in the RVESR. Furthermore, it is demonstrated that sediment transport of the shallow can be evaluated reasonably well using a Shields parameter modified to take into account pore-water pressure on the surface layer of the shallow, and consequently it is essential to consider the pore-water pressure when assessing sediment transport and resulting topographic change of the shallow.

Journal

  • Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)

    Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering) 68(2), I_1061-I_1066, 2012

    Japan Society of Civil Engineers

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